This invention relates to a protective circuit system for emergency lights, by which circuit system, the emergency light battery can be effectively protected from being overcharged or overdischarged so as to extend the life span of the emergency light and to save energy as well.
Conventionally, all emergency lights are usually kept in charging condition during a normal electrical supply state until a power failure occurs and emergency lighting is then effected which usually lasts till the voltage level of the battery installed in the emergency light drops to zero value. In order to prevent this overcharging and overdischarging operations, the known emergency lights are generally provided with a circuit arrangement for performing a floating charge when the battery thereof is charged to a saturated voltage level and for effecting the cut-off of the current flowing to the load thereof from the battery. Although the floating charge prevents the current of the power source from flowing into the battery, the voltage of the power source thereof still maintains a floating value thereat and continuously charges the battery with pulsating current. As a result, the electrolyte of the battery is kept on evaporating, curtailing the life span of the battery set. On the other hand, the known emergency lights are provided with an overcharging protective device though, it is only effective in a temporary cut-off of the battery power source to the load thereof. The battery parts are still kept in consuming the power of the battery, and damage will be incurred to the battery in case that the ceased charging operation to the battery is prolonged thereat. Therefore, the floating-charge arrangement and the overdischarging device provided in the known emergency lights are imperfect in performing preventive functions in the emergency lights.